The present invention relates to latch guards for doors and, more particularly, to an interlocking latch guard for obstructing and resisting the unauthorized entry of an inwardly opening locked door.
Conventional door locking mechanisms typically utilize a retractable spring-loaded latch operated by a door knob rotatable from either side of the door. When the door is closed, the latch contacts a latch strike plate causing it to recede within the door until it is aligned with a socket formed within the door jamb or frame. Once aligned, the latch springs into the socket to retain the door in the closed position. The knob typically has a buttom-type locking mechanism on one side which when engaged, prevents the knob from being rotated to retract and disengage the latch from the socket. Hence, the door is locked and cannot be opened. The opposite side of the knob typically has a key mechanism for disengaging the locking mechanism so that the knob can again be rotated to retract the latch from the socket.
Unfortunately, many door locking mechanisms can be violated by techniques commonly used by unwanted intruders. For instance, many latches can be tampered with simply by sliding a flexible strip of material, such as a plastic credit card, between the door and the frame to disengage the latch from the socket, thereby allowing the door to be opened even though the knob is incapable of being rotated. More destructive methods of tampering with the latch include inserting rigid objects, such as jimmy bars or screwdrivers, between the door and the frame to pry the latch from the frame.
The more determined intruder is willing to structurally damage the door or frame to gain unauthorized entry. In this respect, the typical method of entry involves spreading the vertical frames of the door jamb at the level near the latch. The frame of a typical door is constructed of pine wood approximately one inch in width and spaced from a support stud. The latch typically extends into the frame by only one-quarter to one-half of an inch. Thus, the frame itself is not very strong and can be bent or moved fairly easily by these amounts to disengage the latch from the frame. In order to spread the frame, intruders commonly use a car-jack type device positioned horizontally between the vertical frames of the door jamb near the level of the latch. When the jack is cranked, it spreads the vertical frames such that the latch can be removed from the socket and the door opened.
To combat the above-identified problems, so-called latch guards or protectors have been developed. One example of such a device is described in U.S. Pat. No. 3,290,081. The door locking guard illustrated and described in that patent includes a latch plate attached to the door and having an extension protruding beyond the edge of the door. When the door is closed, the extension fits within a groove or channel formed in the door jamb. The channel is formed in a combined guard and latch strike plate recessed in the door stop and jamb. Therefore, one significant drawback with this type of latch guard is that it requires that the door jamb be specially cut or recessed to receive the latch strike plate, and that the door stop be rabbeted to receive the channel portion of the latch strike plate. Also, the door must be cut or recessed to attach the extension member. A similar type of latch guard is shown in U.S. Pat. No. 4,130,311. However, this latch guard also requires that a recess be cut in the door and jamb, or that the entire jamb be made of metal that has been specially configured to form a recessed groove therein.
Another type of prior art latch guard includes a channel attached to the door which engages or interlocks with a plate attached to the door frame. Although this type of latch guard does not require that the door or frame be specially recessed or cut, it has significant additional drawbacks. For instance, the fasteners used to attach the latch guard are sufficiently exposed, even when the door is closed, to allow an intruder with a screwdriver or pliers access to remove the fasteners and hence remove the latch guard. Even if one-way screws are used, they are often susceptible to being removed with pliers or a similar tool. Further, the prior art latch guards of this type position the frame plate fasteners at a significant distance from the door and the interlocking channel. This is a significant drawback since any spreading action applied to the latch guard will be at an angle to the horizontal line of direction of the frame plate fasteners. This causes a greater torque force to be applied to the frame fasteners which is often sufficient to twist or separate them from the frame. Further, the farther the fasteners are placed from the door, the less resistant the latch guard is to the application of a spreading force.
Accordingly, there exists a definite need for a latch guard which is easy to install on the outside surfaces of a door and frame, works on most conventional doors, does not require a specially recessed door or frame or the special cutting of the door or frame, restricts access to the fasteners when the door is locked, minimizes the amount of torque placed on the fasteners when a spreading force is applied to the frame, and which is further resistant to other techniques for forcing latches open. The present invention satisfies these needs and provides further related advantages.